"What's really funny is that today is the actual due date," Arizona manager Torey Lovullo said. "I don't know how often that happens. I know, having been through that, and I'm sure a lot of people have, that the due date's not always accurate, but in this case it was exactly the right day.
"So we'd been preparing for this moment. We'd been in contact with Taijuan, asking how things were going, and everything was fine and trending toward a start [Thursday]. And before he left last night, because we let him go early, he said, 'Everything's fine, doesn't look like it's going to happen and I'll be ready to go tomorrow. And obviously you can see how fast things change."
Patrick Corbin started in Walker's place on regular rest, and was outstanding in 7 1/3 innings of work against the Reds -- allowing just one run while walking one and striking out six in a 12-2 win. Corbin's performance saved the D-backs from having to use Matt Koch, who was called up Thursday to take Walker's spot on the roster, in relief.
"The thing I remember about him from Spring Training is the mound presence, the poise and the ability to follow the game plan, so I'm anxious to see how he's been improving and see where he's at today."
Koch -- who had a 8.47 ERA in 17 innings for Triple-A Reno -- could make a spot start Friday, although Lovullo said after Thursday's game that he hadn't made a decision yet.
"I think he's definitely going to be an option," Lovullo said. "There was no usage today, so I think he's going to be a guy that we will consider. But we haven't determined who will be tomorrow, who will be Saturday yet."
Jeremy Vernon is a reporter for MLB.com based in Cincinnati who covered the D-backs on Thursday.